Advance the iterator and return the next value. Return None when the end is reached.

Return a lower bound and upper bound on the remaining length of the iterator.

The common use case for the estimate is pre-allocating space to store the results.

Chain this iterator with another, returning a new iterator which will finish iterating over the current iterator, and then it will iterate over the other specified iterator.

Example

let a = [0i];
let b = [1i];
let mut it = a.iter().chain(b.iter());
assert_eq!(it.next().unwrap(), &0);
assert_eq!(it.next().unwrap(), &1);
assert!(it.next().is_none());

Creates an iterator which iterates over both this and the specified iterators simultaneously, yielding the two elements as pairs. When either iterator returns None, all further invocations of next() will return None.

Example

let a = [0i];
let b = [1i];
let mut it = a.iter().zip(b.iter());
assert_eq!(it.next().unwrap(), (&0, &1));
assert!(it.next().is_none());

Creates a new iterator which will apply the specified function to each element returned by the first, yielding the mapped element instead.

Example

let a = [1i, 2];
let mut it = a.iter().map(|&x| 2 * x);
assert_eq!(it.next().unwrap(), 2);
assert_eq!(it.next().unwrap(), 4);
assert!(it.next().is_none());

Creates an iterator which applies the predicate to each element returned by this iterator. Only elements which have the predicate evaluate to true will be yielded.

Example

let a = [1i, 2];
let mut it = a.iter().filter(|&x| *x > 1);
assert_eq!(it.next().unwrap(), &2);
assert!(it.next().is_none());

Creates an iterator which both filters and maps elements. If the specified function returns None, the element is skipped. Otherwise the option is unwrapped and the new value is yielded.

Example

let a = [1i, 2];
let mut it = a.iter().filter_map(|&x| if x > 1 {Some(2 * x)} else {None});
assert_eq!(it.next().unwrap(), 4);
assert!(it.next().is_none());

Creates an iterator which yields a pair of the value returned by this iterator plus the current index of iteration.

Example

let a = [100i, 200];
let mut it = a.iter().enumerate();
assert_eq!(it.next().unwrap(), (0, &100));
assert_eq!(it.next().unwrap(), (1, &200));
assert!(it.next().is_none());

Creates an iterator that has a .peek() method that returns an optional reference to the next element.

Example

let xs = [100i, 200, 300];
let mut it = xs.iter().map(|x| *x).peekable();
assert_eq!(it.peek().unwrap(), &100);
assert_eq!(it.next().unwrap(), 100);
assert_eq!(it.next().unwrap(), 200);
assert_eq!(it.peek().unwrap(), &300);
assert_eq!(it.peek().unwrap(), &300);
assert_eq!(it.next().unwrap(), 300);
assert!(it.peek().is_none());
assert!(it.next().is_none());

Creates an iterator which invokes the predicate on elements until it returns false. Once the predicate returns false, all further elements are yielded.

Example

let a = [1i, 2, 3, 2, 1];
let mut it = a.iter().skip_while(|&a| *a < 3);
assert_eq!(it.next().unwrap(), &3);
assert_eq!(it.next().unwrap(), &2);
assert_eq!(it.next().unwrap(), &1);
assert!(it.next().is_none());

Creates an iterator which yields elements so long as the predicate returns true. After the predicate returns false for the first time, no further elements will be yielded.

Example

let a = [1i, 2, 3, 2, 1];
let mut it = a.iter().take_while(|&a| *a < 3);
assert_eq!(it.next().unwrap(), &1);
assert_eq!(it.next().unwrap(), &2);
assert!(it.next().is_none());

Creates an iterator which skips the first n elements of this iterator, and then it yields all further items.

Example

let a = [1i, 2, 3, 4, 5];
let mut it = a.iter().skip(3);
assert_eq!(it.next().unwrap(), &4);
assert_eq!(it.next().unwrap(), &5);
assert!(it.next().is_none());

Creates an iterator which yields the first n elements of this iterator, and then it will always return None.

Example

let a = [1i, 2, 3, 4, 5];
let mut it = a.iter().take(3);
assert_eq!(it.next().unwrap(), &1);
assert_eq!(it.next().unwrap(), &2);
assert_eq!(it.next().unwrap(), &3);
assert!(it.next().is_none());

Creates a new iterator which behaves in a similar fashion to fold. There is a state which is passed between each iteration and can be mutated as necessary. The yielded values from the closure are yielded from the Scan instance when not None.

Example

let a = [1i, 2, 3, 4, 5];
let mut it = a.iter().scan(1, |fac, &x| {
  *fac = *fac * x;
  Some(*fac)
});
assert_eq!(it.next().unwrap(), 1);
assert_eq!(it.next().unwrap(), 2);
assert_eq!(it.next().unwrap(), 6);
assert_eq!(it.next().unwrap(), 24);
assert_eq!(it.next().unwrap(), 120);
assert!(it.next().is_none());

Creates an iterator that maps each element to an iterator, and yields the elements of the produced iterators

Example

use std::iter::count;

let xs = [2u, 3];
let ys = [0u, 1, 0, 1, 2];
let mut it = xs.iter().flat_map(|&x| count(0u, 1).take(x));
// Check that `it` has the same elements as `ys`
let mut i = 0;
for x in it {
    assert_eq!(x, ys[i]);
    i += 1;
}

Creates an iterator that yields None forever after the underlying iterator yields None. Random-access iterator behavior is not affected, only single and double-ended iterator behavior.

Example

fn process<U: Iterator<int>>(it: U) -> int {
    let mut it = it.fuse();
    let mut sum = 0;
    for x in it {
        if x > 5 {
            continue;
        }
        sum += x;
    }
    // did we exhaust the iterator?
    if it.next().is_none() {
        sum += 1000;
    }
    sum
}
let x = vec![1i,2,3,7,8,9];
assert_eq!(process(x.move_iter()), 1006);

Creates an iterator that calls a function with a reference to each element before yielding it. This is often useful for debugging an iterator pipeline.

Example

use std::iter::AdditiveIterator;

let xs = [1u, 4, 2, 3, 8, 9, 6];
let sum = xs.iter()
            .map(|&x| x)
            .inspect(|&x| println!("filtering {}", x))
            .filter(|&x| x % 2 == 0)
            .inspect(|&x| println!("{} made it through", x))
            .sum();
println!("{}", sum);

Creates a wrapper around a mutable reference to the iterator.

This is useful to allow applying iterator adaptors while still retaining ownership of the original iterator value.

Example

let mut xs = range(0u, 10);
// sum the first five values
let partial_sum = xs.by_ref().take(5).fold(0, |a, b| a + b);
assert!(partial_sum == 10);
// xs.next() is now `5`
assert!(xs.next() == Some(5));

Apply a function to each element, or stop iterating if the function returns false.

Example

range(0u, 5).advance(|x| {print!("{} ", x); true});

Loops through the entire iterator, collecting all of the elements into a container implementing FromIterator.

Example

let a = [1i, 2, 3, 4, 5];
let b: Vec<int> = a.iter().map(|&x| x).collect();
assert!(a.as_slice() == b.as_slice());

Loops through n iterations, returning the nth element of the iterator.

Example

let a = [1i, 2, 3, 4, 5];
let mut it = a.iter();
assert!(it.nth(2).unwrap() == &3);
assert!(it.nth(2) == None);

Loops through the entire iterator, returning the last element of the iterator.

Example

let a = [1i, 2, 3, 4, 5];
assert!(a.iter().last().unwrap() == &5);

Performs a fold operation over the entire iterator, returning the eventual state at the end of the iteration.

Example

let a = [1i, 2, 3, 4, 5];
assert!(a.iter().fold(0, |a, &b| a + b) == 15);

Counts the number of elements in this iterator.

Example

let a = [1i, 2, 3, 4, 5];
let mut it = a.iter();
assert!(it.count() == 5);
assert!(it.count() == 0);

Tests whether the predicate holds true for all elements in the iterator.

Example

let a = [1i, 2, 3, 4, 5];
assert!(a.iter().all(|x| *x > 0));
assert!(!a.iter().all(|x| *x > 2));

Tests whether any element of an iterator satisfies the specified predicate.

Example

let a = [1i, 2, 3, 4, 5];
let mut it = a.iter();
assert!(it.any(|x| *x == 3));
assert!(!it.any(|x| *x == 3));

Return the first element satisfying the specified predicate

Return the index of the first element satisfying the specified predicate

Return the element that gives the maximum value from the specified function.

Example

let xs = [-3i, 0, 1, 5, -10];
assert_eq!(*xs.iter().max_by(|x| x.abs()).unwrap(), -10);

Return the element that gives the minimum value from the specified function.

Example

let xs = [-3i, 0, 1, 5, -10];
assert_eq!(*xs.iter().min_by(|x| x.abs()).unwrap(), 0);